| 1. |
- Forsberg, Pontus, 1981-, et al.
(författare)
-
Making the diamond vortex phase masks for the METIS instrument
- 2024
-
Ingår i: Diamond and related materials. - : Elsevier. - 0925-9635 .- 1879-0062. ; 146
-
Tidskriftsartikel (refereegranskat)abstract
- Direct observation of exoplanets and proto-planetary disks with the METIS instrument at the Extremely Large Telescope will provide new insights into the processes of planet formation and exoplanet atmospheres. This will be possible thanks to a powerful vector vortex coronagraph that can suppress the starlight to reveal faint signals around it. Here we present the process of making the phase masks at the heart of the coronagraph. These annular groove phase masks consist of deep sub-wavelength gratings in diamond that are etched using inductively coupled oxygen plasma with a strong bias. The METIS instrument requires a wider bandwidth than such components have previously been demonstrated for, leading to a grating design with higher aspect ratio and more vertical walls. To achieve this, the etch mask used for diamond etching was changed from aluminium to silicon and the plasma power was increased. We also improved on our method for reducing the grating depth of finished components to fine-tune them. Together with improved optical testing, this allowed us to produce the best vortex phase masks so far demonstrated for the astronomical N-band.
|
|
| 2. |
- Li, Xu, et al.
(författare)
-
Diamond-like/graphite-like carbon composite films deposited by high-power impulse magnetron sputtering
- 2020
-
Ingår i: Diamond and related materials. - : ELSEVIER SCIENCE SA. - 0925-9635 .- 1879-0062. ; 106
-
Tidskriftsartikel (refereegranskat)abstract
- Diamond-like carbon (DLC)/graphite-like carbon (GLC) composite films were prepared with high-power impulse magnetron sputtering (HiPIMS) using a mixture of Ar and Ne as the sputtering gas. The effect of the Ne fraction in the sputtering gas on the surface morphology, carbon bonding structure, microstructure, mechanical properties, residual stress, and tribological performance of the deposited films were characterized using laser scanning confocal microscopy, Raman spectroscopy, nano-indentation, residual stress tester, and friction and wear testing using a ball-on- plate tribometer, respectively. The films have a composite surface structure consisting of sp(2)-rich GLC microparticles embedded in an sp(3)-rich DLC matrix. Both components can be controlled to some degree by varying the Ne fraction. Specifically, as the Ne fraction is increased, both the number and size of the GLC microparticles decreases, while the sp(3) content increases. The GLC microparticles in the film can reduce the real contact area in friction testing, decreasing the friction coefficient, while the sp(3)-rich DLC phase enables the high hardness and wear resistance of the films. By adjusting the Ne fraction during the HiPIMS process, DLC/GLC composite films with low friction and high wear resistance can be generated.
|
|
| 3. |
- Masys, Sarunas, et al.
(författare)
-
Geometries of defects in nanodiamonds optimized with the low-cost methods : How good are they for the electronic g-tensor calculations?
- 2023
-
Ingår i: Diamond and related materials. - : Elsevier BV. - 0925-9635 .- 1879-0062. ; 136
-
Tidskriftsartikel (refereegranskat)abstract
- The geometry optimization of 30 paramagnetic defects, including biomedically attractive nitrogen-, silicon-, germanium-, and nickel-related color centers, is performed after their incorporation into hydrogenated nano -diamond (ND) of C84H64 size. The main aim is to examine the effectiveness of the low-cost methods, namely, PBEh-3c, r2SCAN-3c, B97-3c, HF-3c, and GFN2-xTB, in reproducing the geometries of these defects basing on the similarity between the results of the subsequent electronic g-tensor calculations. It is revealed that the overall performance of PBEh-3c, r2SCAN-3c, and B97-3c is very alike and can be considered as good, however, none of these "3c" approaches is able to cope with all tested geometries. The results of HF-3c, on the other hand, are disappointing, as this method is outperformed by computationally much more lighter GFN2-xTB. Additional calculations carried out for dangling bonds introduced into hydroxylated and aminated NDs show that all low-cost methods perform reasonably well for this type of defect but the largest quantitative discrepancies once again are demonstrated by HF-3c. The obtained findings lay the foundations for the future studies of larger NDs with the purpose to figure out the magnetic properties dependence on the size of NDs or defect positions within NDs.
|
|
| 4. |
- Mukherjee, Debarati, et al.
(författare)
-
Deposition of diamond films on single crystalline silicon carbide substrates
- 2020
-
Ingår i: Diamond and related materials. - : Elsevier. - 0925-9635 .- 1879-0062. ; 101
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide (SiC) is a wide band gap material that is slowly but steadily asserting itself as a reliable alternative to silicon (Si) for high temperature electronics applications, in particular for the electrical vehicles industry. The passivation of SiC devices with diamond films is expected to decrease leakage currents and avoid premature breakdown of the devices, leading to more efficient devices. However, for an efficient passivation the interface between both materials needs to be virtually void free and high quality diamond films are required from the first stages of growth. In order to evaluate the impact of the deposition and seeding parameters in the properties of the deposits, diamond films were deposited on SiC substrates by hot filament chemical vapor deposition (HFCVD). Before the seeding step the substrates were exposed to diamond growth conditions (pretreatment PT) and seeding was performed with a solution of detonation nanodiamond (DND) particles and with 6-12 and 40-60 mu m grit. Diamond films were then grown at different temperatures and with different methane concentrations and the deposits were observed in a scanning electron microscope (SEM); their quality was assessed with Raman spectroscopy.
|
|
| 5. |
- Wang, Xinchang, et al.
(författare)
-
Effects of urea versus N-2 addition on growth and mechanical properties of HFCVD diamond films on WC-Co substrates
- 2022
-
Ingår i: Diamond and related materials. - : Elsevier. - 0925-9635 .- 1879-0062. ; 125
-
Tidskriftsartikel (refereegranskat)abstract
- Nitrogen doped diamonds with great application potentials can be synthesized by using different doping sources (i.e., urea and N2), effects of which on growth behavior and properties of diamond films on WC-Co substrates were presented in this paper. The doping efficiency of urea was always higher than 0.12, much higher than that of N2 (always lower than 0.04). The sufficient N2 addition could increase growth rate, and induce apparent grain nanocrystallization, by modifying reactant gas phase chemistry. The grain nanocrystallization contributed more to the reduction of the surface roughness, and degradation of the diamond purity and mechanical properties. On the contrary, the urea doping resulted in much less degradation of the diamond purity and mechanical properties, while providing sufficient N incorporations into the diamonds. Besides, urea doping promoted the formation of the diamond (220) planes on the polycrystalline diamond surfaces, which had a close relationship with the actual N doping concentration in the diamond. The controllable adjustment of the growth and properties of diamond films, by selecting the doping source and optimizing the doping ratio, could help to meet distinctive application requirements, and balance the machining efficiency and application performance of diamond coated components.
|
|
| 6. |
- Zhang, Ying, et al.
(författare)
-
Capture of novel sp3 hybridized Z-BN by compressing boron nitride nanotubes with small diameter
- 2022
-
Ingår i: Diamond and related materials. - : Elsevier. - 0925-9635 .- 1879-0062. ; 130
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental synthesis of new sp3 hybridized carbon/boron nitride structures remains challenging despite that numerous sp3 structures have been proposed in theory. Here, we showed that compressed multi-walled boron nitride nanotubes (MWBNNTs) and boron nitride peapods (C60@BNNTs) with small diameters could transform into a new sp3 hybridized boron nitride allotrope (Z-BN). This strategy is considered from the topological transition point of view in boron nitride nanotubes upon compression. Due to the increased curvature in compressed small-diameter MWBNNTs, the uncommon 4- and 8-membered rings in Z-BN could be more favorably formed. And the irreversible tube collapse is proved to be a critical factor for the capture of the formed Z-BN, because of the competition between the resilience of tube before collapse and the stress limitation for the lattice stabilization of Z-BN upon decompression. In this case, Z-BN starts to form above 19.0 GPa, which is fully reversible below 45 GPa and finally becomes quenchable at 93.5 GPa. This collapse-induced capture of the high-pressure phase could also be extended to other tubular materials for quenching novel sp3 structures.
|
|
